1. Field of the Invention
The present invention relates to bedsprings, especially box springs for mattresses and spring modules for use in such box springs. More specifically, the present invention relates to the spring module which may be attached to a box spring frame at various locations in order to locally vary the stiffness or firmness of the box spring at that location.
2. Description of Related Art
Typically, a box spring for a mattress comprises upper and lower frames which are interconnected by helically or spirally coiled springs that are spaced over the full area of the box spring. This whole assembly is enclosed in a fabric or foam and fabric covering and is used to support a mattress upon a bed frame.
In addition to the typically used coil springs, other forms of bed springs are known. For example, in U.S. Pat. No, 2,578,331 of Calvin F. White, a bedspring is disclosed wherein the top and bottom frames are interconnected by a multiplicity of C-shaped semicircular elements formed of sinusoidal wire. The resilient elements are arranged in parallel rows with the concave faces of adjacent rows oriented in opposite directions and with the spring elements on one side of the longitudinal center line of the assembly oriented oppositely to those on the opposite side of the longitudinal center line of the assembly.
Another substitute for the typical spirally or helically coiled springs used in box springs for mattresses is the bent wire spring module of the Hagemeister Pat. No. 4,684,111. The spring module of this patent, in front view, has a rectangular appearance with elongated vertical sides interconnected by shorter top and bottom sides. The top and bottom sides are attaching elements comprised of spaced parallel links of wire joined by diagonals and are connected to the respective top and bottom frames by staples or clips. The vertically oriented parallel sidewalls, when viewed in side elevation, are comprised of first, transversely-spaced, parallel, oppositely-inclined, upwardly-extending legs; second transversely-spaced, parallel, oppositely-inclined, downwardly-extending legs; third transversely-spaced, parallel, oppositely-inclined legs that are inclined in an opposite direction from the first and second legs, and fourth legs interconnecting the first legs to the third legs and the second legs to the third legs. The first, second and third legs are of substantially the same length and the fourth legs are disposed in spaced, parallel relation, and are substantially vertical so that the overall appearance is of a single positive and negative phase of a trapezoidally-shaped wave form. This spring module is designed to yield by bending of the legs relative to each other.
It also known how to variously construct springs for use in a box spring so as to provide for softer or stiffer (firmer) yielding characteristics. However, whether softer or stiffer springs have been used, the practice has been to utilize in any given box spring, springs of a uniform firmness so as to produce a softer or firmer support for a mattress that is uniform across the area thereof. On the other hand, it is desirable to be able to selectively produce a localized stiffening of the support for a mattress at various locations, which locations may differ, depending upon the use of the particular box spring. However, a spring module which is optimally usable for producing such a localized stiffening of a mattress box spring, from the standpoints of ease of manufacture and assembly and cost, has heretofore been unknown, and single strand heavy wire stiffeners as have been used extending parallel to the coil springs have suffered several drawbacks. Since these heavy wire stiffeners are made for much heavier wire than the conventional mattress coil springs, they are difficult to attach to the mattress frame in a manner which will assure lateral stability. They also have substantially no resiliency and therefore are prone to break when subjected to impact or heavy loads. Thus, the need exists for such a spring stiffening module that may be selectively and easily inserted between the coil springs of otherwise conventional mattress box spring assemblies which has both lateral stability as well as resiliency.